In a narrow sense, wireless network optimization refers to finding a cause of degradation of network quality through a parameter analysis and a hardware check of an currently operating network, performing a parameter modification, a network structure adjustment and a device configuration adjustment, etc., thereby greatly benefiting from the existing network resources, guaranteeing high-quality operation of a system and achieving a highest profit with a lowest investment.
In a general sense, wireless network optimization includes various aspects ranging from determination of network size, network capacity and capacity expansion scheme, to site location selection and network construction, and further to network parameter configuration. Each step performed during the wireless network optimization may be associated with network quality and affect development of the network. Typically, a network optimization can be divided into the following three stages:
(1) determining the capacity of the wireless network and the requirements on the capacity expansion of the wireless network;
(2) selecting a location for a site and constructing the site according to the geographic features of the region in which the wireless network is located;
(3) configuring parameters for the wireless network.
The stages (1) and (2) constitute a wireless network planning stage mainly for planning the specific distribution of network architecture, and the stage (3) is a wireless network configuration stage for implementing a wireless coverage. Each of the three stages is highly important. In the case that requirements on engineering quality are met in the stages (1) and (2), the stage (3) becomes particularly important.
During the process of existing wireless network optimization, from someone's viewpoint, the further a base station covers, the larger the signal-receiving area is. Therefore, in order to meet the requirements on wireless coverage, parameters such as antenna height and transmission power of base station, generally intend to be larger than normal, which though meets the coverage requirements, brings an immeasurable negative effect.
Taking a Code Division Multiple Access (CDMA) network as an example, the coverage distance of a base station is determined by such factors as the location of the base station and the density of sites. The coverage distance should be proper, neither too long nor too short. However, in order to meet the requirements on wireless coverage, a base station covers a distance actually much further than it is supposed to, and thus a mobile terminal far away from the base station can receive from the base station a signal with strength higher than a strength threshold of the mobile terminal signals. At this time, the mobile terminal sends a pilot measurement report, in which the phase of the cell with respect to the newly detected base station is carried, to its serving base station. Then, according to the phase of the cell with respect to the newly detected base station sent by the mobile station, the serving base station calculates a pseudo random code (PN) of the cell in which the new base station is located by dividing the phase by 64, wherein PN indicates an identifier of a cell in CDMA network, and a cell is associated with a PN. Then, the base station conducts a search in the neighboring cell configuration table to find a neighboring cell corresponding to the calculated PN, and establishes new channel resource for the mobile terminal in the neighboring cell. The neighboring cell configuration table is created based on distances between cells and the direction angles of cells. Specifically, the distances between cells should be as short as possible, and neighboring cells are preferred. Also, the direction angles of cells should be opposite to each other, that is, cells should have as many overlapping coverage areas as possible, so that a mobile terminal moving in a cell can receive a signal from another cell easily. Generally, a base station may enable a mobile terminal to handover to a new cell by sending cell handover indication information to the mobile terminal. However, if the newly detected cell is a cross-cell-coverage cell (i.e., a cell which has a larger coverage area than it is supposed to), and the active set cell which is serving the mobile terminal does not configure the newly detected cell, but configures another cell which has a same PN as that of the newly detected cell as a neighboring cell, the mobile terminal may detect a signal from the base station in newly detected cell, however, the serving base station will determine the target cell for handover add as the another cell having the same PN, leading to an error handover add and thus a call drop of the mobile terminal which severely affects user experience. The term “handover add” means, a serving base station establishes two-channel resources for a mobile terminal moving to the boundary of its serving cell, which are the channel resources of the serving cell and the channel resources of the cell to be hand over, respectively.
FIG. 1 shows an example of the cross-cell coverage of a cell, it can be seen from FIG. 1 that a mobile terminal initiates a call through a Base Transceiver Station (BTS) 4 and detects, during the communication, a signal from a cell of a BTS1, which provides cross-cell coverage and thus is not configured as a neighboring cell by the BTS4. After detecting the signal from the cell of the BTS1, the mobile terminal sends a pilot measurement report to the BTS4. The BTS4 finds, through calculation, that the PN of the cell of the BTS1 is PN2, and then conducts a search in the neighboring cell configuration table of the cell to find that the PN of the cell of a BTS3 is also PN2. Accordingly, the BTS4 incorrectly establishes new channel resources for the mobile terminal in the cell of the BTS3, while the signal actually detected by the mobile terminal is one from the cell of the BTS1. As a result, an error handover performed by the BTS4 causes a call drop of the mobile terminal.
In view of the above, it remains a problem needing an urgent solution how to effectively avoid the cross-cell coverage of a cell.